You have to pay for a (legit) MS Office key. Your Windows key is only for the operating system. You can probably get one off the net somewhere but I'm not sure on the best places to find one these days. Will it not open in Open Office? Failing that, have you tried Google Spreadsheets? Perhaps it will open in that.
Thanks Graham
No it just corrupts in open office (others i use are fine)
Will give google spreadsheets a try, thanks